Fraction of Nitric Oxide in Exhaled Breath.

Nitric oxide (NO) is an odorless gaseous molecule important for biological functions including regulation of vasodilation, smooth muscle relaxation, neurotransmission, platelet aggregation inhibition, and airway epithelial barrier function. It was first discovered in exhaled breath by Gustafsson and colleagues in 1991. However, interest in NO in respiratory medicine escalated following 2 successive independent reports, 1 showing elevated levels of NO in the exhaled breath of individuals with asthma and another demonstrating a decrease in exhaled NO in response to inhaled corticosteroid use. More than 2000 papers evaluate the use of the fraction of NO in exhaled breath, in lung disease.